1. Field of the Invention
This invention is directed generally to optical signal channel selector apparatus for instrumental analysis systems utilizing multiple channels for carrying optical signals and more particularly relates to an optical signal channel selector apparatus adapted for use in a multiple optical fiber sensor system.
2. Description of Related Art
Optomechanical systems for transmitting optical signals are well known in the art and include general classes of optical elements such as light reflectors, light filters, lenses, and optical fibers. Although optical signals from laser sources have been used in telecommunications to carry vast amounts of information over optical signal channels for great distances, optical signals of broader ranges of light wavelengths have also recently been used in optical fiber based analyte sensors employing light absorbance dye indicators or fluorescent dye indicators.
Heretofore in analytical instruments employing optical fibers to carry multiple optical signals, switching between uses of an optical channel as an input signal channel transmitting one wavelength range of light and an output signal channel transmitting a different wavelength range of light has generally been accomplished by pulsing input signals and mechanically interfacing the optical channel with one or more optical filter blocks, which typically involved a mechanical arrangement of solenoids or stepper motors for manipulation of the necessary optical elements for transmission of selected wavelengths of light to be transmitted or detected. Problems such as optical switching noise due to oscillation of moving optical elements which reciprocate or move in shutter action, problems in sticking and misalignment of reciprocating or rotating filter element, and cross-talk between channels associated with this type of mechanical switching of optical interface elements can give rise to reduced signal to noise ratios and can generally interfere with the performance of the instrument.
A fluorescent indicator typically utilizes light in one wavelength region to excite the fluorescent indicator dye to emit light of a different wavelength. Such a sensor may for example utilize a single dye that exists in an acid form and a base form, each with a different excitation wavelength.
Extremely fine sensors with multiple optical fibers for carrying excitation signals to a single sensor head and for carrying return fluorescence emission signals from the sensors have now been constructed for in vivo, intravascular monitoring of multiple vital signs of a patient. Heretofore, each type of sensor typically required its own optical fiber or set of optical fibers for carrying excitation and emission signals. Although a single broad spectrum light source can be used for each of the different types of sensors in a multiple optical fiber sensor by rapidly switching optical filters in optical interface blocks to provide an appropriate wavelength range for each type of requisite excitation signal, such switching of optical elements has been cumbersome, slow, and often not precisely aligned.
Blood gas and blood pH analyzers employing multiple optical fiber sensors have been hindered by problems associated with switching filters in a filter wheel or channel switching in optical interface blocks which include solenoids, or other types of linear actuators, or stepper motors for filter wheels, for mechanically switching between the optical channels as different blood parameters are monitored. In such systems, one or more optical channels can be used to transmit an optical signal from a source to the optical fiber sensor, and to convey return signals from the sensor placed within the vasculature of a patient to an optical detector unit to monitor one or more analytes of interest.
Typically, selection of input signals has also involved the mechanical switching of excitation filters at an optical interface between a light source and the optical fiber sensor, and selection of output signals has involved a similar mechanical switching of emission filters at an optical interface between the optical fiber sensor and a detector. Where the same optical fibers are used to carry both input and output optical signals to and from the sensors, pulsing of the input excitation signal allows for the detection of the output emission signal between excitation pulses. Interference of input and output signals within the optical interface blocks during switching, cross-talk between channels, and signal noise associated with the moving parts in the optical blocks, can reduce the accuracy and reliability of blood parameter measurements from such multiple optical fiber sensor systems.
To reduce the incidence and severity of these problems it would be desirable that an optical signal channel selector be provided which closes non-selected optical channels to avoid cross-talk of the optical signals and to reduce signal noise, and that optical interface blocks associated with individual optical fibers have no moving parts. Such an optical signal channel selector would allow the speed of the instrumental analysis to be limited by the analyte sensing method rather than the switching speed of the system, and such solid state optical blocks could be made smaller and with fewer components at reduced cost.